HYROCHLORIC ACID
Hydrogen chloride is agas; its solutions in water are commonly referred to as hydrochloric acid. This monograph covers both forms.
1. Exposure Data
1.1 Chemical and physical data
1.1.1 Synonyms, structura/ and mo/ecu/ar data
Chem. Abstr. Serv Reg. No.: 7647-01-0
Rep/aced CAS Reg. Nos.: 51005-19-7; 61674-62-2; 113962-65-5
Chem. Abstr. Name: Hydrochloric acid
IUPAC Systematic Name: Hydrochloric acid
Synonyms: Anhydrous hydrochloric acid; chlorohydric acid; hydrochloric acid gas;
hydrogen chloride; muriatic acid
HCI
Hei
MoL. wt: 36.47
1.1.2 Chemica/ and physica/ properties
(a) Description: eolourIess or slightly yellow, fuming pungent liquid or colourIess gas
with characteristic pungent odour (Sax & Lewis, 1987; Budavari, 1989; Weast, 1989)
(b) BoiUng-point: Gas, -84.9 °c at 760 mm Hg (101 kPa); constant boiling azeotrope
with water containing 20.24% Hei, 110 °c at 760 mm Hg (Weast, 1989)
(c) Me/ting-point: anhydrous (gas), -114.8 °e (Weast, 1989); aqueous solutions,
-17.1 °e (10.8% solution); -62.25 °C (20.7% solution); -46.2 °C (31.2% solution);
-25.4 °C (39.2% solution) (Budavari, 1989)
(d) Density: Aqueous solutions, 39.1 % solution (15 °C/4 °e), 1.20 (Budavari, 1989);
constant boilng HCl (20.24%), 1.097 (Weast, 1989)
(e) Specific volume: Gas, 1/47-1/52 gll (LindelUnion Carbide eorp., 1985; Matheson
Gas Product, 1990; AlphagaslLquid Air Corp., 1991; Scott Specialty Gases, 1991)
if Solubilty: Soluble in water (g/100 g water): 82.3 at 0 °C, 67.3 at 30 °e; methanol
(g/100 g solution): 51.3 at 0 °c, 47.0 at 20° e; ethanol (g/100 g solution): 45.4 at
o °c, 41.0 at 20°C; diethylether (gIlOO g solution): 35.6 at 0 °e, 24.9 at 20 °e
(Budavari, 1989); and benzene (Weast, i 989)
(g) VolatiUty: Vapour pressure, 40 atm (4 MPa) at 17.8 °e (Weast, 1989)
- 189-
190
lAe MONOGRAHS VOLUME 54
(h) Conversion factor: mg/m3 = 1.49 x ppma
1.1.3 Technical products and impurities
Hydrochloric acid as an aqueous solution is available in several grades (technical, food
processing, analytical, commercial, photographic, water white) as 20 °Bé (31.45% Hei),
22 °Bé (35.21 % Hei) or 23 °Bé (37.1 % HCI), with the following specifications (mg/kg):
purity, (20 °Bé) 31.45-32.56%, (22 °Bé) 35.21-36.35%, (23 °Bé) 36.5-38.26; sulfites, 1-10
max; sulfates, 1-15 max; iron (as Fe), 0.2-5 max; free chlorine, 1-30 max; arsenic (see lARe,
1987),0.01-1 max; heavy metals (as Pb), 0.5-5 max tluoride, 2; benzene (see IARC, 1987),
0.01-0.05 max; vinyl chloride (see lARe, 1987), 0.01-0.05 max total tluorinated organIc
compounds, 25.0 max; toluene (see IARC, 1989),5.0 max bromide, 50 max; ammonium, 3
(Dow ehemical USA 1982, 1983; Atochem North America, 1986a,b; American National
Standards Institute, 1987; Vista Chemical Co., 1987; BASF Corp., 1988; Du Pont Co., 1988;
BASF Corp., 1989; Dow ChemIcal USA 1989; BASF Corp., 1990; Occidental Chemical
Corp., 1990).
Hydrogen chloride is also available as a liquefied gas in electronIcs grade with a purity of
99.99% and the following impurity limits (ppm): nitrogen, 75; oxygen, 10; carbon dioxide, 10;
and hydrocarbons, 5 (Dow Chemical USA 1990).
1.1.4 Analysis
Methods have been reported for the analysis of hydrochloric acid in air. One method
involves drawing the sample through a silica gel tube, desorbing with sodium bicarbonate/sodium carbonate solution and heat and analysing for chloride ion with ion chromatography.
The lower detection limit for this method is 2 ¡.g/sample (ElIer, 1984). A similar method
entails collecting a sample from the stack and passing it through dilute (0.1 N) sulfuric acid.
The chloride ion concentration is analysed by ion chromatography, with a detection limit of
0.1 ¡.g/ml (US Environmental Protection Agency, 1989).
Hydrogen chloride can be detected in exhaust gas (stack emissions) by: the ion-selective
electrode method (absorb in dilute potassium nitrate solution and measure potential
difference); sIlver nitrate titration (absorb in sodium hydroxide solution, add silver nitrate
and titrate with ammonium thiocyanate); and a mercuric thiocyanate method (absorb in
sodium hydroxide solution, add mercuric thiocyanate and ammonium iron(III) sulfate
solutions and measure absorbance of ferrIc thiocyanate) (Japanese Standards Asociation,
1982).
1.2 Production and use
1.2.1 Production
ln the fifteenth centuiy, the German alchemist Valentin heated green vitriol (iron(II)
sulfate, FeS04. 7HiO) with common salt (sodium chloride) to obtain what was then called
'spirit of salt'. ln the seventeenth century, Glauber prepared hydrochloric acid from sodium
chloride and sulfurIc acid. ln 1790, Davy established the composition ofhydrogen chloride by
acalculated from: mg/m3 = (molecular weight/24.45) x ppm, assuming normal temperature (25 0c) and
pressure (760 mm Hg (101.3 kP))
HYDROCHLORie ACID
191
sythesizing it from hydrogen and chlorine. ln the same year, Leblanc discovered the process
named after him for the production of soda (sodium carbonate), the first stage of which is to
react sodium choride with sulfuric acid, liberating hydrogen chloride. This was first
considered an undesirable by-product and simply released into the atmosphere in large
amounts. ln 1863, English soda producers were compelled by the Alkali Act to absorb the
hydrogen chloride in water, which quickly led to large-scale industral use of the acid
produced. Excess hydrogen chloride that could not be used as hydrochloric acid was oxidized
to chlorine (Austin & Glowacki, 1989).
Following the development of the chlor-alkali electrolytic process early in the twentieth
century, the industrial sythesis of hydrogen chloride by burning chlorine in hydrogen gas
became an important route. This method generates a product of higher purity th
an that
based on the reaction between chloride salts and sulfuric acid or sodium hydrogen sulfate.
These processes are being superseded, however, with the availability of large amounts of
hydrogen chloride that arise as by-products of chlorination processes, such as the production
of vinyl chloride from ethylene (Leddy, 1983; Austin & G lowacki, 1989).
Hydrogen chloride can thus be formed according to the following reactions: (1) sythesis
from the elements (hydrogen and chlorine); (2) reaction of chloride salts, particularly sodium
chloride, with sulfuric acid or a hydrogen sulfate; (3) as a by-product of chlorination, e.g., in
the production of dichloromethane, trichloroethylene, tetrachloroethylene or vinyl chloride;
(4) from spent pickle liquor in metal treatment, by thermal decomposition of the hydrated
heavy metal chlorides; and (5) from incineration of chlorinated organic waste. By far the
greatest proportion of hydrogen chloride is now obtained as a by-product of chlorination.
The degree of purification required depends on the end-use. Recovery from waste materials
(Methods 4 and 5) is becoming increasingly important, whereas the amount generated by
Method 2 is decreasing (Austin & Glowacki, 1989).
Many impurities in hydrogen chloride gas (e.g., sulfur dioxide, arsenic and chlorine) can
be removed by adsorption on activated carbon. As use of the chlorination by-product process
increases, removal of chlorinated hydrocarbons from hydrogen chloride gas or hydrochloric
acid becomes of greater practical relevance. Gaseous hydrogen chloride can be purified by
low-temperature scrubbing with a high-boilng solvent, which may be another chlorinated
hydrocarbon (e.g., hexachlorobutadiene (see IARC, 1979) or tetrachloroethane), or with
special oil fractions. ehlorine may be removed with carbon tetrachloride (see IARC, 1987),
in which it is more soluble than is hydrogen chloride gas. Hydrochloric acid, used as su
ch or
for generation of hydrogen chloride, contains mainly volatile impurities, including chlorise can be removed from the acid by stripping. An inert gas
nated hydrocarbons, and the
stream, which results in lower energy consumption, can be used for stripping, although
heating the gas is preferable for environmental reasons. lnorganic impurities, in particular
iron salts, are removed by ion exchange (Austin & Glowacki, 1989).
Worldwide production of hydrochloric acid in 1980-90 is shown in Table 1. The numbers
of companies producing hydrochloric acid/hydrogen chloride are shown in Thble 2.
192
IAC MONOGRAHS VOLUME 54
Table 1. 'Iends in production of hydrochloric acid (thousand tonnes) with time, 1980-90
Country or region
Australia
Canada
China
France
Gennanya
Italy
1980
1981
1982
1983
63
177
55
11n
59
186
1292
135
1483
674
889
700
886
84
60
170
1583
673
898
NA
NA
NA
570
36
565
33
551
179
137
184
117
191
118
2620
2335
2223
lapan
Mexico
Thiwan
United Kigdom
USA
687
47
1984
1985
1986
1987
57
58
161
158
54
153
NA
NA
NA
NA
767
954
656
943
626
929
NA
NA
NA
NA
511
79
521
212
130
2239
241
156
549
63
228
549
83
242
647
988
679
543
153
157
117
251
174
254
2189
2718
77
2478
1988
1989
199
62
69
180
64
180
NA
164
NA
NA
NA
100
692
956
635
90
565
571
742
637
118
255
176
2928
NA
NA
217
234
162
2124
68
980
From Anon. (1984a,b, 1986, 1987, 1988, 1989, 199, 1991); NA, not available
lZigures prior to 199 are for western Gennany only.
Table 2. Numbers of companies in different countries or regions in
which hydrochloric acid/hydrogen chloride were produced in 1988
Country or region
Country or region
No. of
companies
lapan
USA
Gennany (western)
Italy
Spain
India
B rail
United Kigdom
Australia
Mexico
Canada
France
Argentina
Sweden
Switzerland
Yugoslavi
Thiwan
Bangladesh
Belgium
China
Finland
Israel
Pero
No.
32
27
Portugal
Thailand
Thrkey
3
Austri
2
13
Greece
12
Pakistan
Romania
South Africa
2
2
15
13
11
11
Bulgari
3
3
2
2
10
8
7
7
Egyt
6
5
Indonesia
Republic of Korea
1
5
5
4
3
3
3
3
Kuwait
New Zealand
1
3
of
companies
Chile
Colombia
Norwy
Philppines
Saudi Arbia
Singapore
USSR
Venezuela
3
From Chemical Infonnation Servces (1988)
1
1
1
1
1
1
1
1
1
1
1
1
166
2882
187
675
HYDROeHLORie AeID
193
1.2.2 Use
Hydrochloric acid is one of the most important basic industrial chemicals. A major use is
in the continuous pickling of hot rolled sheet steel; it is also used widely in batch pickling to
remove mil scale and fluxing, in cleaning the steel prior to galvanizing and other processes. It
is widely used in the production of organic and inorganIc chemIcal products: Inorganic
chlorides are prepared by reacting hydrochloric acid with metals or their oxides, sulfides or
hydroxides. Hydrochloric acid has long been used in the production of sugars and, more
recently, of high fructose corn syrup. It is also involved in the production of monosodium
glutamate, for acidizing crushed bone for gelatin and in the production of soya sauce, apple
sweetener and vegetable juice. It is used to increase production of oil and gas wells by
acidizing and formation fracturing and cleaning and by cleaning and descaling equipment.
Acidizing reduces resistance to the flow of oil and gas through limestone or dolomite
formations. Inhibited hydrochloric acid is used to remove sludge and hard-water scale from
industrial equipment, ranging from boilers and heat exchangers to electrIcal insulators and
glass. Hydrochloric acid has been used in the extraction of uranium, titanium, tungsten and
other precious metals. It is used in the production of magnesium from seawater, in water
chemistry (from pH control to the regeneration ofion-exchange resins in water purification),
brine purification and in pulp and paper production (Sax & Lewis, 1987; Dow Chemical
USA, 1988; Austin & Glowacki, 1989; Budavari, 1989).
1.3 Occurrence
1.3.1 Naturaloccurrence
HydrochlorIc acid is produced by hum
an gastric mucosa and is present in the digestive
systems of most mammals. The adult human gastric mucosa produces about 1.5 1 per day of
gastric juices with a normal acid concentration of 0.05-0.10 N (Rosenberg, 1980).
Natural sources of hydrogen chloride may make an important contribution to atm
ospheric hydrogen chloride. Hydrogen chloride is emitted from volcanoes; total world emissions of hydrogen chloride from this source are very uncertain but have been estimated at
0.8-7.6 milion tonnes per year. Methyl chloride, produced in the sea by marine plants or
mIcroorganisms and on land during the combustion of vegetation, reacts with OH radicals in
the atmosphere to generate hydrogen chloride. Worldwide natural sources produce about
5.6 milion tonnes of methyl chloride per year, equivalent to about 4 milion tonnes hydrogen
chloride. Hydrogen chloride is also produced from the reaction of sea-salt aerosols with
atmospheric acids (Lightowlers & Cape, 1988).
1.3.2 Occupational exposure
Occupational exposure to hydrochloric acid is described in the monograph on
occupational exposure to mists and vapours from sulfuric acid and other strong inorganIc
acids (pp. 44-47). Hydrochloric acid occurs in work-room air as a gas or mist. Duringpickling
and other acid treatment of metals, the mean air concentration of hydrochloric acid has been
reported to range from ~ 0.1 (Sheehy et aL., 1982) to 12 mg/m3 (Remijn et al., 1982). Mean
levels ;: 1 mg/m3 have been reported in the manufacture of sodium sulfate, calcium chloride
and hydrochloric acid, in offset printing shops, in zirconium and hafnium extraction and
during sorne textile processing and laboratory work (Bond et a/., 1991).
IAC MONOGRAHS VOLUME 54
194
1.3.3 Ai,
ln areas influenced by marine air masses, displacement reactions between either sulfuric
acid or nitric acid and aerosol chlorides, such as sea salt, can be an appreciable source of
hydrochloric acid (Harrson, 1990).
Atmospheric levels of hydrogen chloride in Europe and in Michigan, USA, are
summarized in Thble 3 (Kamrin, 1992). Ambient concentrations are generally in the range of
0.4-4 l.g/m3.
Table 3. Atmospheric levels of hydrogen chloride
Lotion
Season
Sampling
duration
range Üi.g/m3)
AlI
Weekly
0.07-0.3
United Kingdom, rural
Summer
2-4 h
United Kigdom, rural
AlI
AlI
Daily
Weekly
1h
Daily
1-3
0.3-2
Martime, background
Concentration
Europe
United Kingdom, urban
Switzerland
Dübendod, Switzerland, urban
Dubendod, Switzerland, rural
Po River, ltaly, rural
Ljubljana, Yugoslavia, urban
Apri 1982
Winter 1985
March 198687
0.3-1.
0.2-3
0.1--.5
0.1--.5
November 1984
February 1985
Iiz, Austri, urban, industrial
Summer 1985
Winter 1983-84
Northern, rural
South Haven, urban
Ann Arr, urban
0.2-3
0.03-3
Winter 198687
Vienna, Austri, urbn
Dortmund, Gennany, urban
Michigan, USA
0.6- 1.2
September-October 1980
Daily
Daily
Daily
Daily
Daily
Winter 1983-84
Weekly
July 199
August 199
6h
Daily
0.2- 1.6
0.1-1.5
0.3-11
0.1--.5
0.5-2
0.1-2
From Kamri (1992)
The main anthropogenic sources of hydrogen chloride in the troposphere are the
burning of coal and the incineration of chlorinated plastics, such as polyvnyl chloride. U Dder
conditions tyical of a modern coal-fIred combustion plant, approximately 80 ppm (119
mg/m3) of hydrogen chloride are contributed to the stack gas for each 0.1 % chlorine iD the
coaL. Hydrogen chloride may be an important determinant of precipitation acidity close to
incinerators and coal-burning plants (Cocks & McElroy, 1984).
Estimated annual emissions ofhydrogen chloride in the United Kingdom in 1983 (total,
260 000 tonnes/year) by source were: coal burning, 92%; waste incineration, 6%; and
atmospheric degradation of chlorinated hydrocarbons, automobile exhausts, glass making,
fuel oil combustion and steel pickling acid regeneration, 1 %. Similarly, in western Germany,
power stations and industral furnaces produced 81.4% of hydrogen chloride emissions,
wate incineration produced 17.5% and other sources only 1.1% (Lightowlers & Cape,
1988).
HYDROeHLORie AelD
195
ln comparison with the emissions of sulfur dioxide (3.7 milion tonnes/year) and
nitrogen oxides (1.9 milion tonnes/year) in the United Kingdom, hydrogen chloride is a
minor source of potential atmospheric acidity, contributing only 4% of the total potential
acidity compared to 71 % from sulfur dioxide and 25% from nitrogen oxides. ln western
Europe as a whole, hydrogen chloride contributes less than 2% of the total potential acidity,
whereas sulfur dioxide contributes 68% and nitrogen oxides 30% (Lightowlers & Cape,
1988).
Estimated emissions of hydrochloric acid from coal burning, waste incineration and
total emissions in 12 western European countries in the early 1980s are presented in Thble 4
(Lightowlers & eape, 1988).
Table 4. Estimated emissions ofhydrogen chloride from two
sources in 12 European countries (thousand tonnes/year)
Country
Source
Coal buming
Austri
Belgium
Denmark
Ireland
France
Gennanyo
lta1y
Netherlands
Norway
Spain
Sweden
Switzerland
Total
0.5
14
4.3
Waste incineration
1.
5.9
6.2
2.1
50
93
21
o
64
9.4
0.5
45
2.6
0.7
10
1.4
240 (63%)
14
15
2.2
4.7
12
140 (27%)
From Lightowlers & Cape (1988)
OWestem part only
ln 1989 in the USA, total air emissions ofhydrochloric acid/hydrogen chloride were estimated to be approximately 27 552 tonnes from 3250 locations; total ambient water releases
were estimated to be 1389 tonnes; total underground injection releases were estimated to be
136 440 tonnes; and total land releases were estimated to be 1926 tonnes (US National
Library of Medicine, 1991).
Hydrochloric acid differs from sulfurIc acid and nitric acid in that it is emitted into the
atmosphere as a primary pollutant and is not formed by atmospheric chemistr. Oxidation of
sulfur dioxide and nitrogen oxides tyicallyproceeds at approximately 1 and 10% per hour or
less, respectively. Over appreciable distances from a major source of
aIl three pollutants
(e.g., a power plant), hydrochloric acid may therefore predominate, even though it comprises
only a small percentage of the total potential acidity (Harrison, 1990).
A municipal incinerator in Newport News, VA, was studied over a four-day period in
1976 to evaluate gaseous emissions when wet chemical and electro-optical methods were
196
lAe MONOGRAHS VOLUME 54
used. Hydrogen chloride concentrations in the stack gas averaged 25.1 ppm (37.4 mg/m3;
range, 12.5-56.7 ppm (18.6-84.5 mg/m3D. The authors compared their results with those
from studies of simIlar facilities (ppm (mg/m3D: New York eity, NY, 41-81 (61-121);
Brooklyn, NY, 64.3 (95.8); Babylon, NY, 217-248 (323-370); Hamilton Avenue, NY, 45-89
(67-133); Oceanside, NY, 96-113 (143-168); Flushing, NY, 38-40 (57-60); Yokohama,
J apan, 280 (417) (large amounts of industrial plastic wastes incinerated at this source) and
Salford, United Kingdom, 227 (338). The authors noted that use of a water scrubber
appeared to provide an effective means of removing hydrochloric acid (J ahnke et al., 1977).
Emissions from a municipal waste incinerator fired by water wall mass and by fuel
derived from refuse contained hydrochloric acìd at concentrations of 22-336 ppm (33-501
mg/m3); emission rates were 0.8-27.0 kg/h (0.2-3.3 g hydrochloric acid/kg of refuse burned)
(Nunn. 1986).
The exhaust from a space shuttle launch in which a solid rocket fuel was used contained
approximately 60 tonnes of hydrochloric acid (Pellett et aL., 1983). Partitioning of hydrochloric acid between hydrochloric acid aerosol and gaseous hydrogen chloride in the lower
atmosphere was investigated in the exhaust cloud from a solid fuel rocket in humid ambient
air. HydrochlorIc acid was present at 0.6- 16 ppm (0.9-24 mg/m3); the partitioning studies
indicated that unpolluted tropospherIc concentrations of hydrochloric acid (-c 1 ppb (-c 1.5
iig/m3D would be in the gaseous phase except under conditions of very high humidity
(Sebacher et al., 1980).
Thermal degradation products of polyvnyl chloride food-wrap film were studied under
simulated supermarket conditions, using a commercial wrapping machine with either a
hot-wire or a cool-rod cutting device. At 240-310 °e, hydrogen chloride is the major volatile
thermal degradation production: mean emissions were 3-59 iig/cut (total range, 1-81
iig/cut) when the hot-wire cutting device was used; hydrogen chloride was not detected when
the cool-rod cutting device was used. Other compounds found were the plasticizer (di(2ethylhexyl)adipate, di(2-ethylhexyl)phthalate, acetyl tributyl citrate), benzene, toluene,
acrolein and carbon monoxide (Boettner & BaIl, 1980).
1.4 Regulations and guidelines
Occupational exposure limits for hydrochlorIc acid or hydrogen chloride ln some
countries and regions are presented in Table 5.
Table S. Occupational exposure IImits and guidelines for hydroride
chloric acidlhydrogen chIo
Country or region
Year
Concentration
InterpretationQ
(mg/m3)
Australia
Austria
Belgium
B rail
Bulgaria
Chile
China
199
1982
199
1978
1977
1983
1979
7
7
7.5
5.5
1WA
1WA
5
5.6
1WA
15
Ceiling
Ceiling
Ceiling
1WA
HYDROCHLORIC ACID
197
Table 5 (contd)
Country or region
Year
Concentration
Interpretationa
(mg/m3)
Czechoslovaki
199
5
10
Denmark
Egyt
Germany
Finland
France
Hungary
India
Indonesia
Italy
Japan
Mexico
Netherlands
Norwy
Poland
Romania
Sweden
Switzerland
Thiwan
United Kingdom
USA
ACGIH
NIOSH
OSHA
USSR
Venezuela
Yugoslavia
199
7
1967
15
199
199
199
199
1983
1978
1978
199
1983
1986
199
199
7b
7b
STL
Ceiling
Ceiling
Ceiling
7
7
4
7.5
1WA
7
1WA
7
7
Ceiling
Ceiling
5
1WA
STEL
199
199
8
199
199
1989
Ceiling
1WA
1WA
STL (15 min)
7.5
10
199
STL
5b
1975
1981
1WA
7.5
15
7b
7
7
7.5
7
7
Ceiling
Ceiling
Ceiling
STEL
Ceiling
1WA
STEL (10 min)
Ceiling
Ceiling
Ceiling
STEL
199
5
1978
1971
7
7
1WA
7
1WA
Ceiling
From Cook (1987); US Occupational Safety and Health Administration (OSHA)
(1989); American Conference of Governmental Industnal Hygienists (ACGIH)
(199); Direktoratet for Areidstilsyet (199); US National Institute for Occpational Safety and Health (NIOSH) (199); International Labour Office (1991)
ar A 8-h time-weighted average; STEL, short-term exsure limit
hski irtant notation
ln 1961, the US Food and Drug Administration lIsted hydrogen chloride as Generally
Recognized as Safe when used as a miscellaneous or a general-purpose food ingredient, with
the limitation that it be used as a buffer and neutralizing agent. ln 1977, it was reclassified as a
multiple-purpose food substance with the same limitation. ln 1984, itwas also regulated as a
food additive to be used to modify food starch and in the manufacture of modified hop
198
lAe MONOGRAHS VOLUME 54
extact. It was listed as an optional ingredient in the following food standards: acidified milk,
rd cottage cheese, tomato paste, tomato
purée and catsup (US Food and Drug Administration, 1984). Hydrochloric acid is currently
approved by the US Food and Drug Administration (1984, 1989, 1990) for the same uses,
tes (paste, pulp, purée).
acidified low-fat milk, acidified skim milk, dry cu
except for tomato concentra
The US Environmental Protection Agency has established a limit for emissions of
hydrogen chloride from hazardous waste incinerators at a mass rate of 4 pounds (1.8 kg) per
hour or 1 % of the hydrogen chloride entering the pollution control equipment (Shanklin
et al., 1990).
2. Studies of Cancer iD HumaDS
2.1 Cohort studies
ln a follow-up study of workers with potential exposure to acrylamide in four US
chemical plants, Collns et al. (1989) reported an excess of lung cancer at one of the facilities
studied. The excess was due partly to an increased number of lung cancer deaths (11)
observed among men who had worked in a muriatic acid (hydrochloric acid) department.
(The Working Group noted that the expected numbers were not reported. J
ln the study of Beaumont et aL. (1987) of 1165 male workers employed in 1940-64 in
three US steel-pickling operations for at least six months (described in detail on p. 83), a
subset of 189 workers had been exposed to mists of acids other than sulfuric, which were
primarily of hydrochloric acid. An excess risk for lung cancer was seen (standardized
mortality ratio (SMR), 2.24 (95% confidence interval (ei), 1.02-4.25); 9 deaths). The excess
persisted for workers who had been employed in 1950-54 when other steelworkers were
used as a control for socioeconomic and life-style factors su
Ci, 1.06-3.78).
ch as smoking (SMR, 2.00; 95%
ln the study by Steenland et al. (1988) of the same cohort (described on pp. 83-84), an
excess of incident cases of laiygeal cancer was observed in steel picklers ((relative risk, 2.6;
95% ei, 1.2-5.0); 9 cases). Two of the cases had been exposed only to acids other than
sulfuric, and three had been exposed to a mixture of acids. (The Working Group noted that
confounding by exposure to sulfuric acid could not be ruled out.)
2.2 Case-ontrol studies
A case-control study of primary intracranial neoplasms conducted at a US chemical
plant (Bond et aL., 1983), described in detail on p. 161, found no association with anyexposure to hydrogen chloride (odds ratio, 1.40; 90% Ci, 0.70-2.80, using the first control group;
odds ratio, 1.02; 90% CI. 0.81-1.29, usingthe second control group). The odds ratio for
exposure to hydrogen chloride for people who had been employed for 1-4 years was 2.02
(90% ei, 0.5-8.1); no association was seen for individuals who had been employed for ). 20
years.
ln a case-control study of renal cancer (Bond et al., 1985, see pp. 161-162), the odds
ratios for exposure to hydrogen chloride were 0.90 (90% Ci, 0.44-1.83) in comparison with
the first control group and 0.86 (90% ei, 0.40-1.86) in comparison with the second (12
cases).
HYDROCHLORie AeID
A
199
case-control studyoflung cancer, nested in a cohort of 19608 men employed at a Dow
fur dioxide
chemical plant (Bond et al., 1986), is described in detail in the monograph on sul
(p. 162). The risk associated with exposure to hydrogen chloride was 1.02 (95% ei,
0.77-1.35; 129 cases); the risk was essentially the same when exposures that had occurred
within 15 years of the date of death of the cases were ignored (0.92; 95% CI, 0.68-1.24; 108
cases). The work histories of the 308 cases of lung cancer and 616 controls in this study were
augmented with 8-h time-weighted average exposures to hydrochloric acid for each job
(0,0.2-0.3 ppm (0.3-0.5 mg/m3), 0.9-2.0 ppm (1.3-3.0 mg/m3) and 2.2-5.1 ppm (3.3-7.6
mg/m3D (Bond et al., 1991), and several exposure measures were developed: duration of
exposure, a cumulative exposure score, highest average exposure categoiy achieved during a
career. ln addition, a latency analysis was done excluding aIl exposures that had occurred
within 15 years of the death of the worker. Smoking histories were available for about 71 % of
the cases and 76% of the controls, based on telephone intervews conducted with the subjects
themselves or with a proxy. ealculation of Mantel-Haenszel adjusted relative risks revealed
no association between any of the measures of exposure used and lung cancer. (The Working
Group noted that the methods used may not have been optimaL.)
ln the population-based case-control studyofSiemiatycki (1991), described in detaIl on
p. 95, no association was found between aH cancers of the lung and exposure to hydrogen
chloride (7% life-time prevalence of exposure for the population). The odds ratio for oat-cell
carcinoma of the lung in exposed workers was 1.6 (19 cases; 90% CI, 1.0-2.6); for workers
exposed at the substantial level, the odds ratio was 2.1 (8 cases; 90% ei, 1.0-4.5). ln an
analysis restricted to the French-Canadian subset of the study population and population
controls, the odds ratio for non-Hodgkin's lymphoma was 1.6 (90% Ci, 1.0-2.5; 18 cases),
and that for rectal cancer was 1.9 (90% Ci, 1.1-3.4; 18 cases).
3. Studies of Cancer in Experimental Animais
3.1 Inhalation exposure
Rat: Three groups of 100 male Sprague-Dawley rats, nine weeks old, were unexposed
(colony con
troIs), exposed by inhalation to air (air con
troIs) or exposed to 10.0 :f 1.7
(standard deviation) ppm (14.9:l 2.5 mg/m3) hydrogen chloride (purity, 99.0%) for 6 h per
day on fIve days per week for life (maximum, 128 weeks). Mortality did not differ significantly
between the treated and the air control groups (t test). No preneoplastic or neoplastic nasal
lesion was observed in any group, but hyperplasia of the laryx and trachea was observed in
treated animaIs (22/99 and 26/99, respectively). Tumour responses were similar in the
treated and control groups, the total incidences of tumours at various sites being 19/99,25/99
and 24/99 in treated, air control and colony control animaIs, respectively (Sellakumar et al.,
1985). (The Working Group noted that the experiment was not designed to test the
carcinogenicity of hydrogen chloride and that higher doses might have been tolerated. i
3.2 Administration with a known carcinogen
ne weeks old, were exposed by
inhalation for 6 h per day on fIve days per week for life (128 weeks) to: (i) a mixture of 15.2
Rat: Five groups of 100 male Sprague-Dawley rats, ni
20
IAe MONOGRAHS VOLUME 54
ppm (18.7 mg/m3) formaldehyde (purity unspecified) and 9.9 ppm (14.8 mg/m3) hydrogen
chloride (purity, 99.0%), premixed before entiy into the inhalation chamber (average
concentration of bis(chloromethyl)ether, which can form from hydrogen chloride and
formaldehyde in moist air (see IARC, 1987), -: 1 ppb (4.7 l1g/m3J) (Group 1); (ii) a
combination of 14.9 ppm (18.3 mg/m3) formaldehyde and 9.7 ppm (14.5 mg/m3) hydrogen
chloride, mixed after entr into the inlet of the inhalation chamber (Group 2); (iii) 14.8 ppm
ride
(Group 4); or (v) air (sham-exposed controls; Group 5). A comparable group of rats (Group
(18.2 mg/m3) fonnaldehyde (Group 3); (iv) 10.0 ppm (14.9 mg/m3) hydrogen chIo
troIs. From week 32, mortality in Group 1 was significantly
6) served as unexposed colony con
higher (J -: 0.05; t test) than that in groups 2-4. Tumours of the nasal mucosa ocurred only
in groups exposed to formaldehyde (groups 1-3), the numbers oftumour-bearing rats being
56/100 (13 papilomas/polyps, 45 squamous-cell carcinomas, one adenocarcinoma and one
fibrosarcoma) in Group 1, 39/100 (11 papilomas or polyps, 27 squamous-cell carcinomas
and two adenocarcinomas) in Group 2 and 481100 (10 papilomas or polyps, 38 squamouscell carcinomas, one fibrosarcoma and one mixed carcinoma) in Group 3. The average
latency to tumour appearance was 603-645 days, and there was no remarkable difference
among the groups. Statistical analysis of the tumour response (Peto 's log rank test) revealed a
significantly increased response in Group 1 as compared to Group 2 (p -: 0.001) and as
compared to Group 3 (p -: 0.025). The authors suggested that formation of alkylating agents
by the reaction between hydrogen chloride and formaldehyde was a possible explanation for
the higher incidence in Group 1. Tumour response in organs other than the nose did not
differ significantly between treated and control groups: the total incidences of tumours at
other sites in groups 1-6 were 221100, 12/100, 101100, 19/99,25/99 and 24/99, respectively
(statistical method unspecified) (Sellakumar et al., 1985).
4. Other Relevant Data
4.1 Absorption, distribution, metabolIsm and excretion
4.1.1 Humans
Because it is highly soluble in water, hydrogen chloride is nonnally deposited in the nose
ogy to sulfur dioxide (see p. 96),
deeper penetration into the respiratoiy tract can be expected at high ventilation rates. As
and other regions of the upper respiratoiy tract. By anal
with aerosols in general, air flow velocity and the aerodyamic diameter of the particles are
important detenninants of the deposition of hydrogen chlopde aerosols. The acidity within
the mucous lining of the respira
tory tract may be neutralized, as with sulfuric acid.
Hydrochloric acid is a nonnal constituent of human gastrc juice, in which it plays an
important physiological role. The healthy stomach is adapted to deal with the potentially
damaging effects of exposure to the acid. The toxicity ofhydrochloric acid after inhalation or
ingestion is due to local effects on the mucous membranes at the site of absorption.
Absorption, distrbution, metabolism and excretion of acids and chloride ions have not been
studied in relation to toxicology, but these processes are well known from hum
an physiology.
Ingestion by healthy volunteers of hydrochloric acid at 50 mM/day for four days resulted
in a fall in blood ánaurinaiy urea, with a concomitant rise in urinary excretion of ammonia
(Fine et al., 1977).
HYDROeHLORie AeID
201
4.1.2 Experimental systems
The absorption, distribution and excretion of hydrochloric acid are similar in humans
and other mammals. Following intravenous infusion of 0.15 M hydrochloric acid into rats (50
ml/kg bw per hour) and dogs (20 ml/kg bw per hour), urinary excretion of the chloride ion
was increased in both species (Kotchen et al., 1980).
4.2 Toxic effects
4.2.1 Humans
Effects of industrial exposures were summarized by Fernandez-eonradi (1983).
Exposure to hydrochloric acid can produce burns on the skin and mucous membranes, the
the solution. Subsequently, ulceration may
occur, followed by keloid and retractile scarring. Contact with the eyes may produce reduced
vision or blindness. Frequent contact with aqueous solutions ofhydrochloric acid may lead to
tory tract, causing larygitis, glottic oedema, bronchitis, pulmonary oedema and death. Dental decay, with changes
th, and related digestive diseases
severity ofwhich is related to the concentration of
dermatitis. Vapours of hydrogen chloride are irritating to the respira
in tooth structure, yellowing, softening and breaking of tee
are frequent after exposures to hydrochloric acid.
Kamrin (1991) estimated that the no-effect level for respiratory effects in humans would
be 0.2-10 ppm (0.3-14.9 mg/m3). Respiratory syptoms were reported in 170 fire fighters
who were exposed to hydrogen chloride produced during thermal degradation of polyvnyl
chloride. (The Working Group noted that other chemicals were present.) The symptoms
d, and post-mortem examination demonstrated severe pulmonary haemorrhage, oedema and pneumonitis (Dyer &
included chest discomfort and dyspnoea. One fatal case was reporte
Esch, 1976).
ln one of eight asthmatic volunteers exposed to an aerosol of unbuffered hydrochloric
acid at pH 2 for 3 min during tidal breathing, airway resistance was increased by 50%.
Bronchoconstrction was increased in aIl eight subjects after inhalation of a mixture ofhydrochloric acid and glycine at pH 2 (Fine et aL., 1987).
Dental erosion of the incisors was observed in 90% of picklers in a zinc galvanizing plant
in the Netherlands, who spent 27% of their time in air containing concentrations of hydrogen
chloride above the exposure limit (7 mg/m3) (Remijn et al., 1982).
Dyphagia and transient ulceration of the oesophagus with luminal narrowing are
usually observed following ingestion of hydrochloric acid (Marion et al., 1978; Zamir et al.,
1985; Subbarao et al., 1988).
4.2.2 Experimental systems
Application of 10 il hydrochloric acid to the comea of rabbits caused desquamation of
the surface epithelial cells at concentrations of:: 0.001 N (Brewitt & Honegger, 1979).
A decreased respiratory rate was observed in Swiss Webster mice exposed to hydrogen
chloride at concentrations above 99 ppm (148 mg/m3) in a study of exposure to 40-943 ppm
(60-1405 mg/m3). The return to control values was slow after exposure to 245 ppm (365
mg/m3) and above (Barrow et al., 1977).
The 30-min Leso for gaseous hydrogen chloride were estimated to be about 4700 ppm
(7000 mg/m3) for rats and 2600 ppm (3870 mg/m3) for mice and those for aerosols of
202
lAe MONOGRAHS VOLUME 54
hydrogen chloride to be about 5700 ppm (8500 mg/m3) for rats and 2100 ppm (3130 mg/m3)
for mice. Moderate to severe alveolar emphysema, atelectasia and oedema of the lung were
observed (Darmer et al., 1974). AlI of a group of Swiss Webster mice died or were found
moribund after exposure to hydrogen chloride at 304 ppm (453 mg/m3), which is near the
concentration that reduces the respira
tory rate by 50% (309 ppm (460 mg/m3)), for 6 h per
day for three days. Respiratory epithelial exfoliation, erosion, ulceration, necrosis and less
pronounced lesions in the olfactory epithelium were observed (Buckley et aL., 1984).
No pathological change or change in respiratory parameters was seen in guinea-pigs
exposed to hydrogen chloride at 15 mg/m3 for 2 h per day on five days per week for seven
weeks, compared to control animaIs (Oddoy et al., 1982). ln guinea-pigs exposed by
inhalation to hydrogen chloride at 1309-5708 ppm (1950-8505 mg/m3), the LCso for a
30-min exposure was about 2500 ppm (3800 mg/m3) (Kirsch & Drabke, 1982).
ln rabbits and guinea-pigs exposed to 0.05-20.5 mg/l (50-20 500 mg/m3) hydrogen
chloride for periods of 5 min to 120 h, the lethal dose after 30 min of exposure was 6.5 mg/l
(6500 mg/m3); that after 2-6 h of exposure was 1 mg/I (1000 mg/m3). The highest non-lethal
dose for 5 min was 5.5 mg/I (5500 mg/m3), and that for five daily 6-h exposures was 0.1 mg/l
(100 mg/m3) (Machle et al., 1942).
Three weeks after intratracheal instilation of 0.5 ml of 0.08 N hydrochloric acid into
hamsters, a significant increase in secretory-cell metaplasia was observed in the bronchi,
evaluated by estimating the amount of secretory product in the airway epithelium on histological slides (Christensen et al., 1988).
Intratracheal instilation of a single dose of 0.1 N hydrochloric acid (1-3 ml/kg bw) into
dogs increased mortality, lung weight and related histological changes; instilation of 2-3
ml/kg bw usually caused a fall in arterial p02 and lethality (Greenfield et al., 1969). Similar
bits 4 h after instilation of hydrochloric acid (pH
1.5,2 ml/kg bw) (Doddetal., 1976). Instilation ofhydrochloric acid (pH 1.6) at 25 meq/l into
the oesophagus of sodium phenobarbital-anaesthetized dogs induced tritiated thymidine
histological findings were reported in rab
uptake and mitosis in the oesophageal mucosa within 24 h. This concentration was not
suffcient to provoke erosion, ulceration or leukocyic infiltration (De Backer et al., 1985).
ln male adult baboons exposed for 15 min to 0, 500, 5000 or 10 000 ppm (745, 7450 or
14 900 mg/m3) hydrogen chloride, no persistent alteration was observed in pulmonary
function three days or three months after exposure (Kaplan et al., 1988).
Studies in experimental animaIs in vivo and in vitro have been performed to elucidate the
role of hydrochloric acid in the mammalian stomach in inducing peptic ulcers and
oesophagitis. Severe da
oesophagus of rab
mage and increased permeability to H+ ions were observed in the
bits after perfusion in vivo with solutions of hydrochloric acid (40-80
mM/I) (Chung et al., 1975; Orlando et aL., 1981; Kiroff et aL., 1987). Oesophagitis was also
observed in cats treated with hydrochloric acid (pH 1-1.3) for 1 h (Goldberg et al., 1969).
Isolated rat stomach and duodenum treated with 20-50 mM hydrochloric acid for 10 min
mage of the basal lamina (Black et aL., 1985). Oral administration of
0.35 N hydrochloric acid protected the gastric mucosa of rats against 0.6 N HCI-induced
showed extensive da
gastric lesions for 2 h. The pretreatment significantly increased prostaglandin concentrations
in the gastrc fundic mucosa (Orihata et al., 1989).
HYDROCHLORie ACID
203
4.3 Reprouctive and developmental etTects
4.3.1 Humans
No data were available to the Working Group.
4.3.2 Experimental systems
Groups of 8-15 female Wistar rats were exposed to hydrogen chloride at 450 mg/m3 for
1 h either 12 days prior to mating or on day 9 of gestation (Pavlova, 1976). Offspring were
examined for growth and viabilty after birth and also underwent pulmonary, hepatic and
renal tests at two to three months of age. The authors reported that the exposure was lethal to
one-third of the females, and disturbed pulmonary function (decreased oxygen saturation
and increased vital dye absorption), renal function (increased chloride and protein excretion)
were seen in the survvors. Hepatic function was affected only in exposed animaIs. Postnatal
mortalitywas increased in the litters of dams exposed during pregnancy (3 1.9% versus 5.6%),
and the weight of offspring of dams treated before pregnancy was reduced at four weeks after
birth. Renal function was disturbed (increased diuresis and decreased proteinuria in males)
in the group exposed du
ring gestation at two but not at three months of age. Increased
pulmonary sensitivity was reported in male offspring of females exposed either prior to or
during gestation.
4.4 Genetic and related etTects (see also Thble 6 and Appendices 1 and 2)
4.4.1 Humans
No data were available to the Working Group.
4.4.2 Experimental systems
Hydrochloric acid did not induce reverse mutations in Escherichia coli but caused
mutations in 15178Y mouse lymphoma cells at the tk locus.
Hydrochloric acid induced chromosomal aberrations in VÌcia faba, in grasshopper
(Spathostemum prasiniferum) spermatocyes (by injection), in sea urchin spermatozoa and in
cultured ehinese hamster ovary (CHO) cells. There was a threshold in the aberration
response to increasing hydrochloric acid concentration. The effect in eHO cells was
observed in the absence of rat IIver S9 preparations at a nominal hydrochloric acid concentration of 14 mM (pH 5.5) but was greater in the presence of S9, when a nominal hydrochloric
acid concentration of 10 mM (pH 5.8) was required (Morita et al., 1989). The greater effect of
pH in the presence of S9 was due to generation of substances from S9 at low pH, as
demonstrated in experiments in which the pH of medium containing S9 was lowered to 0.9
and readjusted to 7.2 before the cells were exposed. A similar effect was observed in the
absence of S9 in medium submitted to this cycle of pH changes with hydrochloric acid
(suggesting that clastogens may be generated in serum-containing culture medium at low
pH) (AK. Thilager, reported by Brusick, 1986).
Although only results with hydrochloric acid are reported here, similar results were
obtained with other inorganic acids and with acetic acid (AK. Thilager, personal communication reported by Brusick, 1986) and lactic acid (Inga
Ils & Shimada, 1974), indicating that
the hydrogen ion concentration is the most important factor in experiments with acids,
although specific effects of cations cannot be ruled out.
~
Table 6. Genetic and related effects or hydrochloric acid
'lst system
Resulta
Without
exogenous
metabolic
system
ECR, Escherichia coli, (B/Sd-4I1,3,4,5) reverse mutation streptomycinR
ECR, Escherichia coli, (B/Sd-4/3,4) reverse mutation streptomycinR
VFC, Chromosomal aberrtions, Vicia laba root tips
*Chromosomal aberrations, Sphaerechinus granulars spermatozoa
*Chromosomal aberrations, Spathostemum prasiniferum spermatoces
Doseh or pH
With
exogenous
metabolic
system
~
a:
o
0
+
+
+
15.~~
15.~~
0
0
0
pH 4.3
pH 6.0
0
pH4
in vivo
CIC, Chromosomal aberrations, Chinese hamster CHO cells in vitro
GSf Gene mutations, mou
se lymphoma L5178Y ce
lis, tk locus
+
(+ )
Reference
+
+
380.~~
0.~~
~
Demerec et al. (1951)
Demerec et al. (1951)
Bradley
et al. (1968)
Cipollaro et al. (1986)
Manna & Mukherjee
(196)
Monta et al. (1989)
Cifone et al. (1987)
Q +, positive; ( + ), weakly positive; -, negative; 0, not tested; ?, inconclusive (variable response in severa! experiments within an adequate study)
hin-vitro tests, J.g/ml; in-vivo tests, mg/kg bw
*Not displayed on profie
Cì
~
::
en
d
E
~
tT
VI
.i
HYDROeHLORie AelD
205
5. Summary of Data Reported and Evaluation
5.1 Exposure data
Hydrochloric acid is one of the most widely used industrial che
mi
cals. It is used in
pickling and cleaning steel and other metals, in the production of many inorganic and organic
chemicals, in food processing, in cleaning industrial equipment, in extraction of metals and
for numerous other purposes.
Hydrochloric acid may occur in workroom air as a gas or mist. The mean concentration
of hydrochloric acid during pickling, electroplating and other acid treatment of metals has
been reported to range from c: 0.1 to 12 mg/m3. Mean levels exceeding 1 mg/m3 may also
occur in the manufacture of sodium sulfite, calcium chloride and hydrochloric acId, in offset
printing shops, in zirconium and hafnium extraction, and during some textile processing and
laboratory work.
Hydrochloric acid levels in ambient air usually do not exceed 0.01 mg/m3.
5.2 Human carcinogenicity data
One US study of steel-pickling workers showed an excess risk for cancer of the lung in
workers exposed primarily to hydrochloric acid. An increased risk for larygeal cancer was
observed in the same cohort; however, no analysis was performed of workers exposed to
hydrochloric acid. None of three US industiy-based case-control studies suggested an association between exposure to hydrogen chloride and cancers of the lung, brain or kidney. ln
one eanadian population-based case-control study, an increased risk for oat-cell carcInoma
was suggested in workers exposed to hydrochloric acid; however, no excess risk was observed
for other histological tyes of lung cancer.
5.3 Animal carcinogenicity data
ln one lifetime study in male rats exposed by inhalation at one dose level, hydrogen
chloride did not produce a treatment -related increase in the incidence of tumours. Hydrogen
chloride was tested at one dose level in combination with formaldehyde by inhalation
exposure in the same long-term experiment in male rats. Hydrogen chloride did not influence
the nasal carcinogenicity of formaldehyde when mixed with it upon entry into the inhalation
chamber. When the two compounds were premixed before entry into the inhalation
chamber, an increased incidence of nasal tumours was observed over that seen in animaIs
treated with the combination mixed on entr or with formaldehyde alone.
5.4 Other relevant data
ln single studies, hydrochloric acid induced mutation and chromosomal aberrations in
mammalian cells; it also induced chromosomal aberrations in insects and in plants. Hydrochloric acid did not induce mutation in bacteria.
206
lARe MONOGRAHS VOLUME 54
s.s Evaluation 1
There is inadequate evidence for the carcinogenicity in humans of hydrochloric acid.
There is inadequate evidence for the carcinogenicity in experimental animaIs of hydrochloric acid.
Overall evaluation
Hydrochloric acid is not classifiable as to Íls carcinogenicity to humans (Group 3).
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